1. Field of the Invention
The present invention relates to the use of acid-stable proteases in animal feed (in vivo), and to the use of such proteases for treating vegetable proteins (in vitro).
Proteins are essential nutritional factors for animals and humans. Most livestock and many human beings get the necessary proteins from vegetable protein sources. Important vegetable protein sources are e.g. oilseed crops, legumes and cereals.
When e.g. soybean meal is included in the feed of mono-gastric animals such as pigs and poultry, a significant proportion of the soybean meal solids is not digested. For example, the apparent ileal protein digestibility in piglets and growing pigs is only around 80%.
The stomach of mono-gastric animals and many fish exhibits a strongly acidic pH. Most of the protein digestion, however, occurs in the small intestine. A need therefore exists for an acid-stable protease that can survive passage of the stomach.
2. State of the Art
The use of proteases in animal feed, or to treat vegetable proteins, is known from the following documents:
WO 95/28850 discloses i.a. an animal feed additive comprising a phytase and a proteolytic enzyme. Various proteolytic enzymes are specified at p. 7.
WO 96/05739 discloses an enzyme feed additive comprising xylanase and a protease. Suitable proteases are listed at p. 25.
WO 95/02044 discloses i.a. proteases derived from Aspergillus aculeatus, as well as the use in animal feed thereof.
U.S. Pat. No. 3,966,971 discloses a process of obtaining protein from a vegetable protein source by treatment with an acid phytase and optionally a proteolytic enzyme. Suitable proteases are specified in column 2.
U.S. Pat. Nos. 4,073,884, 5,047,240, 3,868,448, and 3,823,072, and 3,683,069 describe protease preparations derived from various strains of Streptomyces and their use in animal feed.
These proteases, however, are not acid-stable and/or are not homologous to the proteases described herein.